29 May 2015

Once charged, the 3S(eries)2P(arallel) Li-po pack from a MacBook Pro, was not too keen to keep the top voltage. Each cell parallel slowly decreased voltage from 4.20 V to 4.05 V or so in a couple of days at rest.

So I plugged my usual discharge load: a 12 V / 5 W automotive lamp. It drained about 350 mA. Then I left it there unattended for a couple of hours when the pack voltage had reached ~11 V.

When I came back I found a very faint lamp and this:

Six heavily inflated Li-po cells!! No heat. No smell (these square cells have a sweet smell when they loose gas - and it's toxic of course!).

Each parallel was at 2V thereabout. I took the pack outside and vented each cell to prevent explosion from excessive pressure. Not a big loss since it would not retain enough energy. I have always admired the battery duration on Apple laptops and I think they did a good optimization job in their energy management processes, both software and hardware. A depleted Apple battery is probably really exhaused and not good for reuse.

Morale. Do use a discharge protection circuit if you care of Li-xy cells!

26 May 2015

A MacBook laptop battery pack came into my hands. Pretty old stuff from 2006, but Li-po, rated at 60 Wh. Maybe I am about to get a new battery pack. Lacking the laptop for proper charging, I had to teardown the object. Pictures below show the process. It is almost impossible to open it in a way that it can be built back, so I used some brute force here and there to get past some resistance.

The MacBook Pro battery from 2006.

The aluminium lid is glued.

Cells are under the black plastic sheet.

Configuration is 3S2P.

Electronics on-board. Promptly discarded.

And finally charging it.

18 May 2015

IoT, Internet of Things, is not rocket science anymore. Grab an ESP8266 WiFi module, a USB-to-serial adapter and few wires later you are programming it through the familiar Arduino IDE. The most annoying part is providing 3.3 V at 300+ mA as power supply. That's about 10 USD if you already have a computer for programming.

For this initial test I am uploading my shack room temperature to thingspeak.com in the "ZYW Home" channel.

The circuit reads temperature every 60 seconds (almost 62 seconds, actually) and uploads it to the cloud. The temperature sensor is a 1-wire DS18B20. The dashboard shows the average temperature in buckets of 10 minutes and how many measurements have been made since power-on.

Incidentally the latter number provides two more information:

power outage at home if "cycles" restart from 1

xDSL outage or problems if there is a gap or no data upload

I want to add another temperature sensor for outside and, when ESP-201 modules will come, a solar panel for reading solar illumination. Since ESP-201 allows deep-sleep state, the whole thing could even be battery powered and solar recharged.

10 May 2015

The Apple PowerBook G4 was a powerful laptop ... in year ~2002. I was given a non-working 12" unit in case I could salvage some parts for my projects. Well, besides the battery pack that still holds the charge and lots of small screws, not much in there can be reused. But I was intrigued to find out how the typical Apple cover pulsing light works. So I started carefully dismantling the laptop until I was left with the metallic cover only.

While I have not really understood where the pulsing light is, I had a bright idea: use the metallic cover as heatsink for 1W LEDs and create a diffused light lamp.

After four LEDs and a little wiring the object finally shone:

The lamp held at about 10cm from the wall

In the beginning I connected the 4 LEDs in series, requiring about 12V 300 mA, but that voltage was a problem for a battery powered object that had to keep the low and sleek profile of the original source. So I rewired LEDs in parallel, and now I can use a 3.7 V LiPo cell that can sustain 1.5 A of current. That's much easier to recharge and doesn't need a booster circuit either.

The lamp with other room illumination.

Battery and (mesy) wiring.

I am really satisfied with the result. In a dark 20 sq.m room the lamp produces enough light for reading. I need to find a simple way to hang it 10 cm or so from the wall and a convenient power switch (now it is a jumper, the blue one in the third picture).

Possible improvements: PWM the current so that intensity and current drain can be reduced; use a microcontroller to control each LED and put up a light show, ...

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